The proposed study is designed to correlate host defense mechanisms with the occurrence of bacterial, fungal, and viral nosocomial infections. Emphasis will be on application of techniques used to investigate antibody responses, cellular immunity, and polymorphonuclear leukocyte function in patients at risk of developing hospital acquired infections. Patients will be studied when they have nosocomial infection, and also following cure. Prospectively, older patients, individuals with diabetes, and recipients of renal allografts will be monitored. The objective will be to determine if assessment of defense mechanisms can effectively predict which patients will be colonized and subsequently infected when admitted to a general medical service.